1. Field of the Invention
This invention relates broadly to surgical instruments. More particularly, this invention relates to an endoscope and endoscopic surgical instruments adapted to be extended into a channel of the endoscope.
2. State of the Art
At the present time there are many instruments made for use in endoscopic medical procedures. Typically, endoscopic instruments are long and flexible cylindrically tubular devices with manually operated handles at their proximal ends and tissue-manipulative cutting, grasping, injecting, or cautery components at their distal ends. Such instruments are introduced into a flexible endoscope which is inserted into the patient through a natural or surgically-created opening. The endoscope includes an elongate portion defining several lumens therethrough and a proximal handle for directing the elongate portion. At least one lumen is provided with an optical imaging system, e.g., a scope, and several lumina or “working channels” are typically provided for extending endoscopic instruments therethrough. The working channel of the endoscope typically consists of a PTFE-lined cylindrical tube passing from the proximal (handle) end of the endoscope to its distal (working) end. Working channels are typically 2 to 4 millimeters in inside diameter.
During the medical procedure, the doctor passes one or more endoscopic instruments through the working channels in order to manipulate the tissue being visualized by the optical system of the endoscope. Usually the doctor must repeatedly manipulate the distal end of the instrument by manually pushing and pulling on the proximal portion of the tubular shaft of the endoscopic instrument near where the shaft enters the handle of the endoscope.
The view through an endoscope is highly magnified when seen on the video monitors typically used for these procedures; a field of view that may be a few millimeters across would be enlarged to several inches on the video screen. Accordingly, the instrument must be moved very precisely in very small increments in order to approximate and treat the tissue being visualized. In fact, the doctor must position the distal tip of the endoscopic instrument within a fraction of a millimeter of the desired location in order to achieve desired results. However, because of friction and backlash in the way the instrument passes through the endoscope, achieving this level of accuracy is difficult. For example, an endoscope several feet long may be positioned in the colon of a patient with the distal end of the endoscope tightly reflexed to visualize a particular area of the ascending colon. In such a position, the endoscope is bent into a very sinuous shape in multiple planes. Since the outside diameter of the endoscopic instrument is significantly smaller (e.g., 2.2 mm) than the inside diameter of the working channel (e.g., 3.2 mm), a large clearance space exists between the instrument and the channel. When the instrument is pulled back, the tension on the instrument causes the instrument to be pulled taught and the instrument naturally assumes the shortest path through the channel. When the instrument is pushed forward, friction causes it to assume the longest path through the channel (that is, the shaft of the instrument must “fill” the working channel before the distal end of the instrument begins to move). As a result, quite a bit of backlash (lost motion) is experienced by the doctor when the doctor tries to manipulate the distal end of the instrument. If it is necessary to pull the tip back a bit, the backlash must first be pulled out before the distal end can be retracted. If the doctor pulls the instrument back a little too far, the doctor must then push it several millimeters forward before there is any motion at all at the distal end. During this manipulation, the endoscopic instrument alternately assumes the longest-path and shortest-path positions within the working channel of the endoscope. If this backlash can be reduced or eliminated, the manipulation of the distal end of the endoscopic instrument can be made much easier and more positive, and the doctor can achieve his desired positioning more rapidly. However, this is not a simple problem to overcome for several reasons.
While the backlash situation described above can be reduced or substantially eliminated if the clearance between the outside of the endoscopic instrument and the inside of the working channel of the endoscope can be reduced, this is not a practical solution. It is often necessary to inject fluid (or to operate suction) through the annular space between these two structures. If the instrument shaft were to substantially fill up the space within the working channel, the backlash would be reduced, but there would be greatly reduced ability to conduct fluid through the working channel around the instrument. In fact, because of the nature of fluid flow, as the aspect ratio of the annular clearance space (the ratio of the thickness of the fluid channel to its circumferential length) becomes small, the impedance to fluid flow grows disproportionately to the reduction in cross-sectional area of the fluid passage.
In addition, as the diameter of the shaft approaches the inside diameter of the working channel, the area of contact between the instrument and the working channel becomes larger, particularly since the working channel is usually made of a relatively soft material, PTFE. This increase in contact area between these parts results in an increase in frictional drag on the instrument when the doctor attempts to move it through the channel.